The invention relates to a brake pad, particularly for rail vehicles, comprising at least two friction material blocks. The invention also relates to a process for manufacturing such a brake pad, and also relates to a brake shoe, particularly for rail vehicles having such a brake pad.
Brake pads are used in pad brakes or pad brake units. Pad brakes are brakes in which a brake cylinder, lever transmission and an adjusting mechanism operate to press a brake pad onto the wheel running surface in order to achieve a braking effect. With respect to the further development of brake pad units in the case of rail vehicles, reference is made to xe2x80x9cBrakes for Rail Vehiclesxe2x80x9d, Handbookxe2x80x94Brake-Related Terms and Values, Knorr-Bremse AG Mxc3xcnchen, 2nd Edition, 1990, Page 41.
The brake pads of the prior art are often constructed as a one piece friction material block. Materials of the brake pads or friction material blocks are perlitic cast iron with lamellar graphite, plastic material consisting of a mixture of different substances in an artificial resin bond or buna bond, or sintered material which consists of finest metal powder, such as iron, copper or nonferrous heavy metal.
U.S. Pat. No. 1,219,824, shows a brake pad which comprises a plurality of friction material blocks which are separated by an elastic layer. The individual friction material blocks are mounted transversely to the longitudinal direction of the brake shoe. As a result of this arrangement, the brake pad experiences only slight expansion changes in the event of fluctuating temperatures.
German Patent Document DE 24 18 024 shows a carbon-containing airplane brake disk consisting of a strong durable center core and brake linings which are fastened on both sides and are made of a light-weight material which is subject to wear. The materials which are subject to wear are connected with the center core by an adhesive layer.
Japanese Patent Document JP 55-97537, shows a brake pad which has a slotted construction in the longitudinal direction for reducing the braking noise. The reduction of the braking noise because the slotted construction allows higher temperatures on the braking area.
German Patent Document DE 30 33 936 shows a brake shoe with several brake pads which can be changed very easily.
British Patent Documents GB K 13850 and GB P 14036 show brake pads having lamellar friction material blocks which are connected on their longitudinal sides to form a brake pad. The brake pads were held together by a bolt connections extending transversely to the disk direction.
With respect to the constructions of brake pads, reference is also made, for example to xe2x80x9cBrakes for Rail Vehiclesxe2x80x9d, Handbookxe2x80x94Brake-Related Terms and Values, Knorr-Bremse AG Mxc3xcnchen, 1990, Pages 22 to 23.
In the case of the above-described pad brake systems according to the prior art, the contact pattern is insufficient because of thermal expansions and axial displacements. In fact, the contact pattern is the poorer, the harder the material of the pad. The poor contact pattern results in the formation of corrugations or in cracking in the wheel running surfaces and therefore generates considerable noise during braking.
It is an object of the invention to provide a brake pad system or a component of a brake pad system by means of which the above-mentioned disadvantages can be overcome.
The brake pad according to the principles of the present invention comprises at least two friction material blocks. The individual friction material blocks are lamellar in shape, and are connected mechanically or by an elastic intermediate layer along their longitudinal sides to form a brake pad. As a result of the elastic intermediate layers between the individual friction material layers or the mechanical connections, the braking noise can be reduced because, during the braking, the friction between the individual friction material blocks absorbs noise energy.
Another advantage of the brake pad according to the invention is the fact that, in the case of a non-uniform wear of the wheel tire or during axial displacements, the individual disk stacks can shift in the vertical direction and thus adapt themselves to the running surface of the wheel, whereby an essentially identical surface pressure is always ensured irrespective of the axial position or the wear.
In a preferred embodiment, the elastic intermediate layer is an adhesive layer. As an alternative, the mechanical connection is a screwed, riveted or form-locking connection, particularly a clamp-type connection.
A brake pad comprises at least two, preferably three to four, disks situated side-by-side. The disks are mechanically or form-lockingly connected with one another along the longitudinal side.
In a preferred embodiment, a holding device fastening the friction material block to a brake shoe is provided for each friction material block. In the case of a lamellar construction of the friction material blocks, each disk has such a holding device on the side facing away from the wheel running surface and facing the brake shoe.
Preferably, the holding devices of the individual friction material blocks have a sheet metal reinforcement with integrated holding angles. The sheet metal reinforcement is non-detachably connected with the individual friction material block or the disk stacks, for example, by gluing. The sheet metal reinforcement transmits contact pressure force from the brake shoe to the friction material blocks and the contact pressure force is therefore introduced from the brake shoe to the brake pad. The holding angles for fix the brake pad on the brake shoe and protect against the falling-out or rattling of the individual friction material blocks.
The holding angles are preferably constructed as U-shaped leaf springs which are part of the reinforcement arranged on the friction material block. The invention also provides a process for producing such a brake-pad. According to the invention, the individual friction material blocks are obtained by being pressed or cut out of plates and are connected by gluing or by a mechanically elastic connection to form a brake pad, so that energy can be absorbed by the connection.
The invention also provides a brake shoe having such a brake pad. The brake shoe has a carrying body, a connection device to the power unit of the pad braking device for operating the brake shoe as well as a friction material block holding device. The friction material block holding device can be a guide rail which extends in the wheel turning direction.
The brake shoe according to the invention is exchangeable with conventional brake shoes because the connection of the inventive brake shoe is analogous to that of the conventional brake shoes.
In order to keep the individual forces of the friction material blocks of the multi-disk brake pad upon the wheel running surface constant, the guide rails may be constructed in the form of a balance beam guide rail system. The balance beam guide rail system supports a relative vertical displacement of the disks of the brake pad. This displacement is perpendicular to the wheel running surface. The balance beam system in combination with the multi-disk brake pad, in which the individual disks can be displaced in the vertical direction as a result of the mechanical or shear-elastic intermediate layer, therefore results in a very good contact pattern. This measure permits a higher loading capacity of the wheels and reduces the formation of corrugations or cracking and thus the development of noise when the wheel is rolling.
Furthermore, the balance beam guide rail system is characterized by an elastic yielding perpendicular to the wheel running surface and can be constructed along the entire curve length of the brake pad in one piece or divided into several areas. Multiple-slot guide rails are also conceivable. Furthermore, the balance beam guide rail system can be composed of individual balance beams, one balance beam being assigned to two friction material blocks respectively. The individual balance beams may be hinged to one another in a form-locking manner to form the balance beam system according to the invention.
Alternatively, the entire balance beam system can be produced as an integrated component, for example, of sectional steel.
In order to ensure that the brake pad will still rest on the wheel running surface, during large lateral displacements of the wheel, the brake shoe laterally has guiding parts toward the wheel face which permit a lateral movement of the brake pad. Preferably, these guide parts are constructed as wear-resistant plates toward the wheel side. In order to be able to carry along the friction material blocks, which are connected with the brake shoe by way of the friction material holding device, synchronously during an axial displacement of the wheel set, it is provided in a special embodiment of the invention that the connecting device to the power unit is further developed such that it permits such a movement. A pendulum suspension of the brake shoe is particularly suitable for this purpose.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.